Method making ferrosilicon alloy

ABSTRACT

Method for producing tough non-friable, non-disintegrating ferrosilicon by the addition of copper to the ferrosilicon in the molten state and controlling the cooling rate of the resultant casting in accordance with the copper content and the calcium and aluminum contents of the casting.

D United States Patent [151 3,660,081

Farrell et al. 1 May 2, 1972 54] METHOD MAKING FERROSILICON [56]References Cited ALLOY UNITED STATES PATENTS [72] Inventors: John W.Farrell, North Tonawanda; Wil- I 2,906,653 9/1959 Peras ..75/125 X l D.F N F 1] b th f "gens agara a 8 3,323,899 6/1967 Forgeng.. ..75/0.53,350,197 10/1967 Beeton ..75/125 X [73] Assignee: Union CarbideCorporation, New York,

N.Y. Primary Examiner-L. Dewayne Rutledge Assistant Examiner-J. E. Legru[22] Filed 1970 Att0rneyPaul A. Rose, Frederick J. McCarthy, Jr. and[21] Appl. No.: 5,766 RobertC. Cummings Related US. Application Data 571 S C Continuation-impart of 6521884, y 12, Method for producing toughnon-friable, non-disintegrating 1967, abandQnedferrosilicon by theaddition of copper to the ferrosilicon in the molten state andcontrolling the cooling rate of the resultant [52] U.S. Cl ..75/ 129,75/123 L, 75/125 casting in accordance with the copper content and thecalci. 39/44 C229 39/54 um and aluminum contents of the casting. [58]Fieldof Search ..75/125,129

4 Claims, 1 Drawing Figure Jttllil :1.:...!1 .bsZcALc/uM h 4 .e w

EQUIVALENT I v o ..1 t V i .0 CALCIUMEQl IIl ALENT g 1 1 i l 1 r l 2 I li 0.30 (I) o o: a: LU ll- 5 1 o r r e\ I MAXIMUM COOLING RATE-'6 PERMINUTE IN RANGE OF 850'C TO 700'C METHOD MAKING FERROSILICON ALLOY Thisapplication is a continuation-in-part of Ser. No. 652,884, filed July12, 1967 now abandoned.

This invention relates to ferrosilicon alloys. More particularly, thisinvention is related to a method for producing ferrosilicon materialwhich is strong, dense, non-friable, and nondisintegrating.

Ferrosilicon is a material widely used as an addition agent in the steelindustry, and is usually produced by smelting a mixture of silica,carbon, and iron-bearing materials to obtain a molten alloy which iscast into shapes which are particulated to obtain the size desired bythe customer.

Since ferrosilicon is often transported considerable distances from thepoint of manufacture to the site of ultimate use, and is commonly storedfor long periods and exposed to the elements during storage, it isimportant that the alloy be tough, non-friable, and non-disintegrating.

These requirements present a substantial challenge since ferrosilicondoes not inherently possess the above characteristics.

Various techniques, such as slow cooling of the as produced ferrosiliconcastings, have been used to improve the toughness of the material andthus reduce friability. However, the problem of self-disintegrationduring extended storage still remains.

Very rapid cooling of as-produced ferrosilicon castings has been foundto significantly suppress self-disintegration; however, such materialsare rendered more friable by this type of treatment.

It is, therefore, an object of the present invention to provide a methodfor preparing ferrosilicon material which is both non-friable andnon-self disintegrating, in addition to being strong and dense.

Other objects will be apparent from the following description and claimstaken in conjunction with the drawings which shows a graph illustratingcooling rates in accordance with the present invention.

A method in accordance with the present invention comprises preparing amolten ferrosilicon alloy containing about 38 to 90 percent silicon;admixing a copper-bearing material with the molten ferrosilicon toprovide between about 0.10 percent and 0.50 percent, and preferably from0.15 to 0.30 percent copper in the molten ferrosilicon; casting andsolidifying the thus treated alloy; and cooling the solidified alloy ata rate such that the amount of zeta phase (Fe Si in the final alloy isnot more than about percent.

The zeta phase, Fe Si which is normally present in substantial amountsin the ferrosilicon alloys hereinabove noted, has been regarded as acause of disintegration in ferrosilicon alloys. Zeta phase, Fe Si can beobserved and the amount present calculated from polished and etchedmicroscopic sections of the alloy in which Fe si appears as a separateand distinct phase. Very slow cooling of the ferrosilicon alloycastings, as previously mentioned, has been found to cause sometransformation of the zeta phase, Fe Si to FeSi Si, and a reduction indisintegration to some extent. However, there is still need for furtherimprovement in disintegration characteristics.

It has now been discovered, as part of the present invention, that byadding copper to the ferrosilicon alloy in the manner hereinafterdescribed, that a ferrosilicon alloy which is both non-friable, andessentially non-disintegrating, can be produced even with the use ofrather rapid cooling rates.

In the practice of a particular embodiment of the present invention,molten ferrosilicon is prepared, e.g., percent silicon, balanceessentially iron, and from about 0.10 to about 0.50 percent, preferably0.15 to 0.30 percent, copper is incorporated in the melt by the additionof elemental copper, e.g., copper clippings, or copper alloys containing10 percent or more copper so as to avoid introducing objectionableamounts of undesired elements into the ferrosilicon.

After adding the copper, the molten ferrosilicon is cast and solidified,and the casting is caused to cool at a rate such that the final materialcontains not more than 10% Fe Si illl It is important that the FegSi5content of the alloy be not more than about 10 percent; otherwise, nosignificant benefit is obtained from the copper addition.

It has further been discovered that, in addition to the copper content,the calcium and aluminum contents of a ferrosilicon alloy significantlyaffect the cooling rate required for providing a material containing notmore than about 10% Fegsl5. Further, the relative proportions of calciumand aluminum in the alloy are significant. That is to say, the presenceof a given amount of calcium in a ferrosilicon alloy requires a slowercooling rate as compared to the presence of an equal content ofaluminum. The calcium actually has an effect of fivefold as compared toaluminum.

Accordingly, in the 30 of the present invention, the maximum coolingrate which is permissable to obtain a ferrosilicon alloy containing notmore than about 10% Fe Si is determined through the use of the graph ofthe drawing by locating the curve on the graph corresponding to theeffective calciumaluminum content of the alloy, the effectivecalcium-aluminum content being %Ca %Al/S. This is referred to herein asthe Calcium Equivalent" content. The maximum cooling rate for such alloyis then determined by the intersection of the copper content of thealloy with the previously determined curve for the Calcium Equivalentcontent of the alloy.

For example, with an alloy containing 0.05% Ca, 0.25% A1 and 0.26% Cu,the 5 Equivalent content 2 0.1% and the maximum cooling rate is 7 C/min.between 850 and 700l0% illustrated in the drawing at A. It can be statedmore generally that for any given copper content, the cooling rateshould be to the left of the curve of the drawing corresponding to theCalcium Equivalent content of the alloy.

The casting cooling rates determined in the foregoing manner have beenfound to ensure substantially complete TABLE 1 Maximum Coating CopperContent Calcium Equivalent Rate in Range of Content% 850C to 700C 0.10.05 l.5per minute 0.1 0.2 .75C per minute 0.1 0.3 0.4C per minute 0.20.05 5C per minute 0.2 0.2 1.5C per minute 0.2 0.3 0.7C per minute 0.30.05 14C per minute 0.3 0.2 5C per minute 0.3 0.3 13C per minute 0.350.05 24C per minute 0.35 0.2 8.5C per minute 0.35 0.3 225C per minute 50.05 53C per minute 50 0.2 22C per minute .50 0.3 C per minuteCopper-containing ferrosilicon prepared in the manner aforedescribed isremarkable in that it is both tough, i.e., nonfriable, andnon-disintegrating.

With further reference to the drawing, the graph shown sets forth themaximum desirable cooling rates for copper-containing ferrosiliconalloys containing 38 to percent silicon and the indicated CalciumEquivalent contents. The cooling rates are for the temperature range ofabout 850 to 700C. since it has been found that this is the range inwhich controlled cooling is the most critical to achieve transformationof Fe,Si in copper-containing ferrosilicon. The cooling rate attemperalnnAiA M- tures above about 850C. and below about 700C. can be asfast (or as slow) as desired.

The following example will further illustrate the present invention.

EXAMPLE I A 65 -pound heat of 50 percent ferrosilicon was prepared froman alloy analyzing 48.3 percent silicon, 0.05 percent calcium, 0.70percent aluminum, 0.0l5'percent phosphorous, and 0.06 percent copper.The metal was cast at 1,300C., in -pound increments, into separateclay-graphite crucibles which had been preheated to 1,000C. No additionswere made to the first crucible and copper additions, as elementalcopper, were made to provide copper contents of 0.16 percent, 0.35percent, 1.04 percent in the metal in the remaining crucibles.Immediately after pouring, all crucibles were buried in sand to producea very slow cooling rate. After cooling to room temperature, thesolidified alloy from each crucible was broken with a hammer and piecesof each sample were exposed to the outdoor atmosphere for 10 days. Atthis time the base alloy sample containing 0.06 percent copper had begunto crumble and was easily abraded by rubbing pieces of the alloytogether. The samples containing 0.16 percent, 0.35 percent, and 1.04percent copper showed no sign of disintegration and were solid, tough,and abrasion resistant.

EXAMPLE II The procedure of Example 1 was followed to provideferrosilicon alloys containing 0.06 percent, 0.15 percent, 0.35 percent,0.55 percent, 0.80 percent and 1.0 percent copper. After 7 days exposureto the outdoor atmosphere, the alloy containing 0.06 percent copper hadnoticeably disintegrated. The other alloys showed no sign ofdisintegration.

EXAMPLE Ill The procedure of Example I was followed in preparingferrosilicon alloys containing (A): 0.008% Ca, 0.22% Al and 0.16% Cu and(B): 0.008% Ca, 0.22% A1 and 0.22% Cu.

Castings prepared from both alloys were cooled in the temperature rangeof 850C to 700C at a rate of 4 to 5C per minute. Alloy (A) containedapproximately 25% Fe,Si,-, while alloy (B) was essentially free of Fe SiIt has also been found that with ferrosilicon alloys which containcopper, but in which the Fe si phase has not transformed, e.g., rapidlyquenched alloys containing 0.16 percent copper, no significantdisintegration tendency is observed although the material is easilyabraded.

In a further embodiment of the present invention, the copper addition ismade to the ferrosilicon alloy by mixing a reducible copper compoundsuch as copper oxide, with a silica-carbon charge. The copper compoundis reduced concurrently with the silica, and copper is therebydirectly'incorporated in the ferrosilicon alloy product.

The percentages given herein and in the claims are all by weight, unlessspecified to the contrary.

What is claimed is:

1. A method for producing an essentially non disintegrating ferrosiliconalloy which comprises preparing a molten ferrosilicon alloy containingfrom about 38 to percent silicon and minor amounts of calcium andaluminum; admixing a copperrich material with the molten ferrosilicon toprovide in the ferrosilicon alloy a copper content of from about 0.10 to0.50 percent; casting and solidifying the thus treated alloy; andcooling the solidified alloy at a rate such that the amount of zetaphase, Fe Si in the alloy is less than about 10 percent.

2. A methodin accordance with claim 1 wherein between about 0.15 and0.30 percent copper is provided in the ferrosilicon alloy.

3. A method in accordance with claim 1 wherein, for a given coppercontent, the solidified copper-containing ferrosilicon is cooled in therange of 850to 750C. at a rate which is in the area to the left of thecurve shown in the graph of the drawing corresponding to the CalciumEquivalent content of the alloy

2. A method in accordance with claim 1 wherein between about 0.15 and0.30 percent copper is provided in the ferrosilicon alloy.
 3. A methodin accordance with claim 1 wherein, for a given copper content, thesolidified copper-containing ferrosilicon is cooled in the range of 850*to 750* C. at a rate which is in the area to the left of the curve shownin the graph of the drawing corresponding to the Calcium Equivalentcontent of the alloy where the Calcium Equivalent % Ca + % Al/5.
 4. Amethod in accordance with claim 1 wherein the copper-rich material is acopper alloy containing at least about 10 percent copper.